Electronic structure of CuAlO2 and CuScO2 delafossites under pressure

The electronic structure of CuAlO 2 and CuScO 2 delafossites is investigated by means of optical absorption measurements under pressure and ab initio band structure calculations. Measurements are carried out on CuAlO 2 monocrystals and pulsed laser deposited CuAlO 2 and CuScO 2 thin films up to 20 GPa. CuAlO 2 is an indirect semiconductor that is stable in the pressure range explored here. The pressure coefficients of the indirect and direct gaps are found to be 15 meV/GPa and 2 meV/GPa respectively. CuScO 2 is a direct semiconductor and the pressure coefficient of the excitonic peak energy is -5.5 meV/GPa. Two reversible phase transitions are observed in CuScO 2 . At 13 GPa the delafossite…